Who is the only English king to be called "great" and why was he given this title?

Alfred had a reputation as a learned and merciful man of a gracious and level-headed nature who encouraged education, proposing that primary education be conducted in English rather than Latin, and improving the legal system and military structure and his people's quality of life. He was given the epithet "the Great" in the 16th century and is the only English monarch to be labelled as such.